(549c) Understanding the Cation-Mixing Mechanism in Ni-Rich Cathodes from First Principles | AIChE

(549c) Understanding the Cation-Mixing Mechanism in Ni-Rich Cathodes from First Principles

Authors 

Xiao, Y., Virginia Tech
Li, X., Columbia Universtiy
Li, Z., Virginia Polytechnic Institute and State University
West, A., Columbia University
Urban, A., Columbia University
The growing demand for high energy density Li-ion batteries requires a move away from conventional Co-containing cathode materials. Although LiNiO2 is chemically similar to LiCoO2 and offers the same theoretical capacity, LiNiO2 and related Co-free Ni-rich cathode materials suffer from degradation during electrochemical cycling that has hindered commercialization. One complication affecting LiNiO2 is the difficulty of synthesizing the material in its ideal stoichiometric composition. In practice, off-stoichiometries (Li1-xNi1+xO2) cannot be avoided. In addition, the formation of structural defects via Li/Ni cation mixing reduces cyclability and leads to poor capacity retention.

We determined the Ni migration mechanism in ideal and defected LiNiO2 using first-principles calculations and identified the energetically most probable pathways for Ni migration and for the phase transition to the spinel structure. Our results show that off-stoichiometries promote the formation of Li/Ni defects. Furthermore, we find that the formation of the spinel phase occurs via a concerted mechanism, which explains why the phase transition is usually not observed during cycling. Our study is a first step towards understanding degradation in Co-free cathodes and underlines the importance of considering defects in materials modeling.